PARTITIONING THE COMPONENTS OF MAXILLARY TOOTH DISPLACEMENT BY THE COMPARISON OF DATA FROM 3 CEPHALOMETRIC SUPERIMPOSITIONS

Using roentgenographic cephalograms from a sample of subjects with met allic implants, appropriately superimposed tracings were used to disti nguish developmental and treatment-associated displacements of the max illary central incisor and first molar associated with ''local'' chang es within the periodontium from ''secondary'' changes which reflect su tural and appositional growth at more distant osseous loci. Tracings w ere superimposed on anterior cranial base (ACB), on the maxillary impl ants only (IMP_MAX), and according to the best fit of maxillary anatom ic structures without reference to the implants (A_MAX). Using the IMP _MAX superimposition, one could measure total local displacement at an y landmark taking into consideration the effects of all appositional a nd resorptive changes on the superior and anterior surfaces of the pal ate, whereas using the A_MAX superimposition one could measure local d isplacement without consideration of surface appositional and resorpti ve changes. If the second of these measurements were subtracted from t he first, the result would be a direct measurement of the effects of s urface appositional and resorptive changes as they are expressed at th at particular landmark. This strategy has enabled us to quantify and r eport the amount of accommodation which occurs at the location of each dental landmark in association with the resorptive and appositional c hanges which occur through time on the superior and anterior surfaces of the hard palate.